DESCRIPTION: (verbatim from application) Although lower extremity muscle strength is a reliable measure of impairment and an index of functional capacity in the elderly, peak power or the maximum capacity to perform muscular work per unit of time may play a more important role in functional independence and disability prevention than muscle strength alone. Recent work from our laboratory suggests that peak lower extremity power, compared to lower extremity strength, is a better predictor of performance-based function and is an independent predictor of self-reported disability in frail elderly women. Although progressive resistance training (PRT) has been effective in significantly increasing muscle strength and size, the effects of PRT on performance-based measures of function have been less dramatic. The proposed study will examine the physiologic and functional effects of a muscle power training intervention in comparison to traditional PRT in a community-based group of elderly men and women with moderate mobility limitation. The proposed study will test the hypothesis that lower extremity peak power training will result in greater improvements in function, as assessed by tests of physical performance, compared to strength training. We propose that the hypothesized mechanisms by which peak power training will exert these effects include: a larger increase in skeletal muscle mass, muscle fiber hypertrophy, an increased in vitro shortening velocity of isolated single fibers with no change in specific force. A randomized controlled intervention trial will be conducted with subjects (N=75) being assigned to a lower extremity (knee and hip extensors) peak power training intervention, PRT, or control group for 3 months. Primary outcomes of interest will be assessed at baseline, and 3 months and include: physiological tests of leg strength, power, and endurance; performance-based functional tests, balance and mobility; biochemical measurements of skeletal muscle biopsies including histochemical and contractile properties; and body composition assessed by dual energy x-ray absorptiometry. The results of this study will have important implications in evaluating the effects of lower extremity power training, a potentially more effective means of modifying the proximal determinants of physical disability in the frail elderly.